Obesity is one of the leading causes of morbidity and mortality in the United States. Unfortunately, the traditional approach to obesity does not achieve satisfactory, sustained weight loss. Alternatively, the most commonly performed bariatric operations result in significantly reduced body weight sustained for at least 15 years and remarkable mprovements in comorbid conditions. The recent growth in the performance of bariatric procedures has been unprecedented, largely influenced by the development of minimally invasive techniques and increased patient and provider awareness of the potential benefits of the procedure. However, the acceptance of the procedure has been limited because of questions regarding its effectiveness in the population at large, public reporting of postoperative deaths and complications at leading medical centers and because of cost control considerations. Assessing the effectiveness and cost-effectiveness of bariatric procedures is problematic because there have been no adequate evaluations of outcome in the general population. Furthermore, the role of these procedures in higher risk patients (i.e older or more debilitated) is even less established. To address the question of bariatric procedure safety, effectiveness and cost-effectiveness we propose the following study utilizing Centers for Medicare/Medicaid Services (CMS) nationwide, Part B claims database. Over 20% of all hospitalized patients are CMS beneficiaries and while only 10% are under the age of 65, this younger, medically disabled group includes many patients who undergo bariatric surgery. The specific aims of this research are to: 1. Determine the population-level risk of adverse outcomes following bariatric surgical procedures. 2. Evaluate patient and provider factors associated with adverse outcome to help individualize risk assessments for patients being considered for bariatric procedures. 3. Perform a modeled cost effectiveness analysis of bariatric procedures compared to non-surgical approaches.